<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<meta name="viewport" content="width=device-width, initial-scale=1">
		<title></title>
		<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
	</head>
	<body>
		<script>
			var a1 = 1;
			function func1(){
				this.a1 = 2;
				console.log(this.a1);
			}

			var func2 = () =>{
				console.log(this.a1)
			}
			function func3(){
				this.say = () =>{
					console.log(this.a1)
				}
			}
			new func1();//2
		    func2();//1
			new func3().say();//undefined
		</script>		
	</body>
</html>